re: the white velvet from RHC, I’m not sure if you are looking at the white velvet with milk choco ganache, which is a recipe for one 9x2 round, or if you are looking at the choco covered strawberry cake, which is a recipe for two 9x2 rounds.
Because Rose’s wedding cake recipes in the Cake Bible make 1.5” layers, I’m thinking we might assume that the sheet cake recipes from the Rose Factor chart also make 1.5” layers. So for a 2” layer you may need about 1/3 more batter. The Rose Factor chart says to use a factor of 3.5-4, and increasing that by a third would give you 4.7-5.3, so if it were me, I’d make a Rose Factor 5 batter with the baking powder from level 6. So you would need a recipe with 500g each of flour and sugar, and 6.25 tsp (2 Tbs plus 1/4 tsp) of baking powder.
I haven’t made this and can’t confirm that that is the exact amount of batter that would give you a 2” high cake, but that’s where I would start if it were me. Perhaps others will chime in if they have experience with the rose factor sheet pans.