Your fat to carbohydrate ratio is ok.
Just try 0.5 % ssl as single emulsifier and upto 1% A4c with 0.2% xanthan.
Try to procure soy protein isolate from solae ( supro series) at 1% level.
The minimum pressure on first stage should be 6500 psi from a Gaulin type homogenizer.( if ur machine can’t achieve this all formulations are useless , and if u can achieve this then u may as well may be able to formulate toppins as low as 12% )
The chilled topping out temperature before packing should not exceed 6 ° C. ( very important for optimum overrun)
( just to say, ingredient companies usually suggest formulations , but they are invariably useless .)
Also use 50% HPKO and 50 % HPKS in total fat utilized
Single use of HpKO will give cracks . The above ratio has a better SFI for whiping cream.
Hope this helps.