Is this the little Parkzone T-28 or a larger glow powered model like the BH T-28?

If it is the Parkzone I'd program the high rates for 100% travel. Then program the low rates for about 1/2 of that. That's what I did on my T-28 and I adjusted from there.

I personally don't think this plane needs any exponential but if you really want to use it, maybe 35% on high rate and 25% on low rate? (Nothing scientific about those numbers, just came up with them).

All of this is just a starting point; I'd find an experienced flyer to take it up and see what he thinks about those settings. He can recommend any necessary changes. After you have some time and experience on the plane you can decide if you want to make any changes to the throws and stuff to suit your liking.

I looked around in the T-28 manual and on the Parkzone site but did not find any control throws listed.