Resource leveling and subsequent float report

Could anyone explain how to get P6 to report the float levels correctly after resource leveling?

An example...

I have two 20d activities of pipe laying, both starting on the same date but both required for commissioning. The current float is reported as 10d and we are ahead of schedule.

I now have one gang to lay the pipes, so the pipe laying activities now take 40d in total (i.e. one after the other), after resource leveling. However, the float is still reported as 10d, even though we are now reporting being 10d late.

What I would like is for P6 to report that my float is now -10d and we are late.

Is it an option I have or have not ticked correctly or can this not be done?

Any help will be greatly appreciated.

Thanks,

Dean.