the A4 will ‘iron out’ the slight tempo variation issues way better than the OT will, especially regarding pickup machines, so if it works for you, it might be best to try making the OT the master - that, of course, may have unacceptable complications, but it’s worth noting - the audio side is ‘elastic’ but the recording side isn’t, so it’s simpler for me to drive the A4 from the OT -that probably doesn’t help with your issue, but you seem to be in the minority using the A4 as master fwiw - that’d probably have been my pref too