Fixed interest loans...

I would say that there is every reason to have the fixed interest loans well represented - because they are the ones with the real security. The variable interest rate would be valuable if the interest rate (within a band) was related to risk - but it is more related to the size of the loan and says very little about relative risk.
The whole loan lenders have a fixed rate on every loan - that does not seem to be a problem.

If worried about a property crash (which I am not) then having too much in that sector may be a worry - but the alternative is unsecured loans. You have to decide which is the frying pan and which the fire.

It does strike me that the whole p2p offering is very new and the rules have not quite yet been bashed out by years of good and bad events. With the property loans via FC I will be interested to see how they do when the final payment is made on a number of them. This may be only a year away. It would be very difficult for FC if the failures were excessive and I am sure that they will be proactive. I get the impression that FC are not as good as protecting investors assets as some of the other p2p firms albeit these firms are much smaller and would not have experienced as much volume.

I hold quite a lot of these both from new and the SM. I do try to diversify them with the more conventional loans. Personally with years of QE I suspect that property assets should not lose their value but there must be risk there.