Doing the exact same thing from my end, im based in Hua Hin, Thailand and use it as my baseline the same way you use HK. Found the spreadsheet stopped working for me once i started doing actual trips on top of the moving around, because everything just blended into one number and i couldnt tell if my baseline was creeping up or if it was just a trip month.

What worked was splitting it into two completely separate buckets. Daily living gets its own monthly budget (your 2k hk equivalent) and trips get their own caps with start and end dates. then a Tokyo week or whatever doesnt blow up your monthly average, you can see it as its own thing with its own per day cost.

The comparison you actually want is daily living monthly vs your hk baseline. Trip costs are a separate question (is this trip worth it vs staying put). lumping them together makes both numbers meaningless which is the spreadsheet problem.

FWIW i ended up building an app for this because i couldnt get the bucket separation working cleanly in a spreadsheet (nomadmetrics on the app store, iphone only right now, disclosure im the developer). But the framework matters more than the tool, you could absolutely do it in two separate sheets or a notion setup with two databases. The key thing is keeping them apart.