That is fairly long grass for a "toy" tank
I have tested mine in almost identical conditions and it is a tough condition for them, the blades of grass confine them from steering easily and the grass seems to me "slippery", denying traction.
My theory(and thats all it is, is a theory) is that certain sizes and proportions of 1/16 scale tanks do better than others on marginal conditions.
My Stug and to some extent, my Pz IV don't do as well in longer grass.
The Panther is better, due to its size and track width but even with 3:1's it has some steering difficulties.
The KT with 3:1's is better than the Panther on grass, likely due to sheer size.
The "stars" of my inventory on longer grass are the two 3:1 equipped Tiger I's. I believe it is due to; their size, wider tracks than anything else I have and they are shorter and wider. I recall reading that for its size, the Tiger I could pivot in place relatively well and this was used to make up for the slower turret traverse; perhaps this ability translates somewhat to the model.
I know for less than ideal ground conditions, I like to use the Tiger I's.
"Luck favours the prepared!."