Does the iOS AVAudioUnitSampler only support a limited number of controllers?

Looks to me like some are (e.g. volume, pan...) but others aren't, despite them being configured (and working on macOS) in the .EXS file using Logic Pro's Sampler MOD MATRIX. I've tried using sendController(), sendMIDIEvent() and MusicDeviceMIDIEvent(). I'm sure the latter worked at some point but could be mistaken. Vaguely recall the AK guys were using this to tweak envelopes in their ROM player.

For example, it would be nice to control one of the filters cutoff frequency via a CC #74 message but I can't seem to get this working at all on iOS.

Question is, basically, am I expecting too much from AVAudioUnitSampler on iOS?