corne,

If you are using 'configuration e' then the tubesheet is integral with channel and the way you have modelled model 2 would match that configuration but,

The sketch you included on the first post suggests that what you have is a tubesheet gasketed both sides which would be 'configuration d'.

Model 1 looks closer to the actual layout, although element 20-30 would be channel side (and not shell side as modelled).