MIA how to ring-fence funds to particular loan ?

Have you checked your settings?
There's been a fair bit gone on to the market over the last couple of days.

The way that loans are allocated to investors is very different now. Everyone who sets a target, and has funds available will get a slice on drawdown, and this will include some users who are simply looking for a place to park their money short-term (for various reasons, including that they'll be reducing the target later in order to diversify as more loans become available).

For loan #150, I didn't have any funds available on drawdown, but my (admittedly very low) target was met during the following few days. If I had a higher target, I'd undoubtedly have received even more chunks towards this, or maybe even still be receiving them.

During the weeks following drawdown, I'd tend to expect a new loan to become harder to get, as the short-term investors exit their positions so that almost all units are then held by long-term investors.

AIUI...  That minimum wouldn't apply if the amount offered is less than £1.  Or if the difference between your target and your holding is less than £1.

Whilst having a 'priority investment' flag sounds nice it could be detrimental to overall investment because it prevents investments in other loans. For example you set a £1000 target for an upcoming loan and set the priority flag, with the loan being relatively small and popular individual lenders only get allocated £100 so you have £900 un-invested. However without the flag you have the possible situation that other lenders will attempt to sell off some of their existing holdings in order to free up cash for the new loan so you could well find that you have invested £1000 in loans that you want just not necessarily the one particular loan, this is particularly so if everyone else is setting the 'priority investment' flag.

The situation becomes worse after the release of the loan if you only £100 of your £1000 target and you don't reset the priority flag as in the worst case situation you could find yourself with a £100 invested and £900 un-invested the whole life of the loan. 

That scenerio was covered in the "grumpnosebest " ideas made earlier, I quote:

I envisage the reserve facility on my MLIA resources being configurable to fund anything in the list of loans on the upcoming list to the limit of the target set. If less than the target were to be allocated, the balance of the reserve on that loan could be returned to the main MLIA stash. I forgot to mention my target of £500 in the imminent Grandgrumps.com Pensioners Aids loan, so my example above would only have £505.99 available for general investment.

Even releasing unallocated cash after the release of the loan does not resolve the whole issue as the most likely time that other existing loans are put up for sale by lender will be just before the release of a new loan by underwriters.

The thing to do is to stop thinking of the MLIA as a conventional P2P platform where you have invest put money in and bid on each new loan, rather you need to think of it in the same vein as the GEIA but with more (manual) controls whereby you can define which loans you don't want to invest in and where you do want to invest the absolute maximum to want to invest. It is then a case of adding funds and letting the platform do the investing. Adding ring fencing only acts to slow the overall investment process, it does not guarantee that you will be allocated your target amount, it just guarantees that your funds will not be invested elsewhere. Extending the £1000 example further: You set a £1000 target for an upcoming loan paying 9.75%, add the £1000 to the MLIA and set the priority flag, meantime someone divests the selves of loan parts in a loan baying 12% which you have set a target for but not the priority flag so now not only do you get only £100 in the prioritized loan due to over subscription you have also ensured that you missed out on picking parts in more lucrative loan.

The method with AC now is to set your own personal limits on how much you are willing to have uninvested and for how long, and judging how fast the platform will absorb the fund so that you can feed in fund at an appropriate rate, and not to worry overly about which loans the platform is investing in within your preset targets.