Since you’re already using a 1.5 cane reed on a Yam 4C I’d say stick with only that. Leave the plastic for the moment. Place the reed on the mpc and adjust on the sax neck blowing an E whilst at the same time keeping a relaxed embouchure, top teeth on the mpc and bottom lip slightly curved onto the bottom teeth. I think your muscle memory needs to forget the plastic. Once you’re happy with your note production stick the neck onto the sax body and play long notes tonguing Low D to high B keeping the same embouchure as when practicing with just the neck; muscle memory should help. Play your scales exercises 20 minutes, break, 10 minutes, break, 10 minutes freeplay. Do not bite to achieve the correct pitch but relax ( for low notes) or tighten ( for higher notes) the embouchure as you play. Stick with that mpc reed combo until you start going sharp because your jaw muscles are becoming stronger, tighter.. ( that will take a few months) Then move onto a 2 cane reed. You shouldn’t have to go above 3 with the 4C. Do not keep switching between different reeds and mpcs when starting. Good tone production is not how wide the tip or how hard the reed are but how your embouchure, breath control and tonguing deliver the note...amongst other things that you will discover on this splendid voyage. Enjoy the adventure.