Length of the TT to your tow vehicle does matter, but there isn't a magic ratio other than shorter is better. IMO, it's just another factor to consider. If you're pushing the weight capacity of the truck, I wouldn't push the length too much either.
Do you have the F150 with the 6.5 foot bed or the 5 foot bed? Reason I ask is that the wheel base on the 6.5 foot bed is basically the same as on the typical F250, which is a good thing. Personally, I'd stay under a 30' travel trailer with a 1/2 ton truck, especially if you have the 5 foot bed. The power and braking should be fine, but I do worry about stability due to cross winds. The 3/4 & 1 ton trucks weigh a lot more and have much stiffer suspensions, so they do a better job at keeping the TT in place compared to a 1/2 ton.
I used to have a 2012 F150 with the 6.5 foot bed and now have a 2013 F250 diesel. The F250 literally weights a ton more than the F150, per Cat scales. That's 2000 more pounds to keep the trailer in place, on top of having a MUCH stiffer suspension.
So bottom line is that the length of TT matters. How much depends on other factors.