Also just tried to set up an expression control in H90 through MIDI using Reflex just in case (I use TRS expression usually), seems to work fine, used following settings

Reflex:

Digital Out 1 (d1)

Chan 4 (H90 channel)

Type 7 (CC#7)

H90:

Preset Exp Pedal Flange

Changed Control Source from Exp Pedal to MIDI CC CC#7