So we have two things going on that we need to understand:
LFE = Low Frequency Effects (your .1 channel) a specific channel encoded with LFE for films.
Then we have Redirected Bass, which works in conjunction with the Crossover you have selected and your L&R Main speakers. These are two very different things but are quite often confused
So your L&R speakers are physically large (and very nice by the way) their frequency response if accurate shows that they have the ability to go quite low, however, a Subwoofer has the ability to go much lower and handle the low frequencies much better, after all that's specifically what it's designed for.
Large speakers, or Full Range speakers as they should really be referred to, have a frequency response of 20Hz to 20kHz.
With your speakers set as Large, essentially what you are telling your AVR is that all bass will be handled by your L&R speakers.
With your speakers set to Small you are essentially telling your AVR that they can't handle the Full Range (even very large floor standing speakers usually can't go low enough at meaningful levels) so we supplement the L&R speakers with a dedicated Subwoofer. When we do this, we need to set a crossover to tell the AVR when to crossover from L&R speakers to the Subwoofer. This is why your crossover setting was grayed out when they were set to Large.
Setting the crossover to get a good blend between your L&R speakers and Subwoofer is the tricky bit. The generally recommended setting as per THX specs is 80Hz, as i don't know how accurate the quoted frequency response of your RP-280F towers are, i would experiment with the 40Hz setting that it has defaulted to when you set your speakers to Small, I'd suggest 60Hz would be a more appropriate figure to try, but this is entirely down to you and how it sounds to your ears.
I must admit i am not an expert in Audyssey, so you may get more help in the dedicated thread.
You may have to run a manual setup as changing what has been set post Audyssey calibration may create problems.
Hopefully this has helped rather than confuse matters even more?
There are lots of useful tips and articles on how to get the best out of your setup, so good luck.