Thanks. Have now tried this. Bike on stand small to small, changed up to middle - no issues at all. tried a few times, different cadences, works.
But, in small to small the rear mech upper section contacts the chain, so I need to lose a link. I'll be swapping small c/r 24 to 26, so that may lift the RD off the chain. As it is, 2nd smallest sprocket i.e. 11>12 gives space between chain & RD.
On small to big, the lower jockey wh is slightly backward of upper wheel.
Be cautious shortening a chain.
The critical factor in determining chain length is that it *must* be long enough to accommodate big-big; otherwise you are into frame-wrecking territory.
Conventional wisdom is to wrap it round big-big without threading through the rear mech, find the shortest it can be made up in this configuration, then add one complete link (eg a half-link inner plus a quick-link outer, same thing.)
Any shorter is dangerous.
Any longer is un-necessary and you might run out of stroke on the rear mech to take up slack.
ETA based on Paul's comment: If the chain length required for safe big-big is too long for the rear mech to take up the slack in small-small, then you have over-reached the spec of the rear mech by quite a large margin. Shimano are quite conservative in their spec, and will accept a bit of tolerance abuse, but in the case I am describing, you need a longer arm mech.
Any other method of sizing the chain is not good enough if it cannot guarantee big-big safely.