[sealevel]

Agreed, you get neither speed nor skill at that point but do get a high probability of missing a reading as the car passes the S/F line.

Cheers!
PS the latter two diagrams remind me of the AC2Car layout of Jame's White Lake F1 circuit

 

[sealevel]

Looks great!
Are you using the stock Scalextric pylons to support the elevated section or did you do something else?

Keep up the good work!
Cheers!