We have a similar problem at our field. There are 2 spots on the field where you get hit. The kicker is it's only on high band and only with Futaba receivers. I assume because all of your xmitters are Futaba you are using the Futaba recievers that came with them.

I fly nine different planes on my Futaba T6xa and T6xas on channel 54 and the two that get hits are the ones with the Futaba receivers. All the others have Hitec Supremes and never get hit. We have other members in the high range and they are guaranteed a hit in these two spots if they have high band Futaba receivers. It doesn't matter what xmitters.

Like yours the hits are quick. You get full throttle and down elevator. Bad combo. We've gotten used to them and laugh about them. They haven't claimed a plane YET.

Another thing about ours is that you have to be headed in one certain direction. We have carried a plane to the "spot" and it will go nuts but if you turn it 20 degress in any direction it stops.

This field has been in use for almost 30 years and this just started this year.