Michael's height is an anomaly that can't be solved, especially with both Castle and Courtney playing him in
Halloween Kills.
I normally try to match the actor height, unless it's superseded by character height.
Since the '78 and 2018 figures represent bookends - the 2018 will soon be sandwiched by the HK version - I wanted them to match regardless.
As you wrote, the extra height helps with the longer, baggier overalls on TOTS' '78.
Since I'm planning on using the green overalls from the Accessory pack I hope they're not going to be too short. 2018 length would be good as I like the way they fit.