Interesting dilemma the pin on boot thing, as pointed out bitlocker protects from the HD being fiddled with outside the machine.
When the machine is under the control of the OS, post pin unlock in your case, the drive is unencrypted including when in sleep mode.
At this point it’s the windows password keeping it safe or some other credential bio or card or whatever.
So I guess it’s at what point you think the laptop is going to get nicked and then what point of attack they are going to use.
Personally I don’t bother with the pin as it’s a pita, and doesn’t really add that much.
The pin isn’t the encryption key, that’s stored in the TPM, it’s just something else to remember or write on a post it stuck to the keyboard.