Regarding having a porch by the entrance (different from just a perch) some people might say will still allow aerial predators easier access inside the box, but I disagree because for one, the height between the roof overhang and the landing board (7") will keep large aerial predators of the likes of owls and red tailed hawks from chilling on the porch. Two, if these large aerial predators wanted to peak their head into the entrance hole of the nestbox they could do it regardless if a porch is present or not by merely digging their claws into any part of the house for support. The wood is soft, it's the non-treated cedar fence boards commonly found in hardware stores such as Home Depot. So I don't think that would be a valid reason to exclude a porch from a kestrel nestbox. Besides, why not give them a place to shield from the sun, rain and harassment from other birds at times? The only problem I can envision at the moment is that if there are too many young kestrels when they find the courage to hop on the porch, not all of them will fit there and thus the one(s) left inside the nestbox might not get a chance to eat. But that's just hypothetical thinking.
Funny thing is that ever since I installed the porch (that is, the protruding landing board with the additional over-reaching roof addon that's on top of the original nestbox roof as the photo shows) a month ago, the kestrels have been perching on the porch about 90% of the time I see them on the nestbox. I find that quite interesting. My reason for installing the porch was from my observations the previous year that during rain events I noticed each time there was a kestrel on the nestbox it would sometimes try its best to shield itself from the rain as much a possible by hugging as close as it could to a bat house mounted on the same post within touching distance from the kestrel nestbox. By the way, the bat house is no longer there on the same post this year as I had the epiphany that having bat and kestrel house like that was not a good idea. So Bat house is now on another post 400 feet away (still no bats in it)
The house floor plan is 8.5"x10", but I wish I had made it 11"x9.5" because if the kestrels have more than three young it's going to get way too crowded towards the latter half of their stay in my humble opinion.
Anyways, just thought I'd share what I was up to kestrel world.