Help with series sorting in Pocketbook

Hello, I have a Pocketbook Touch Lux 5 and I have noticed that in the series that have short novels, the series number does not appear correctly.
I mean if the number of the series is 4.5 only appears the 4 when the calibre if I put 4.5.
Is there any way to display the whole number?
Thanks
PS. Forgive my possible mistakes, English is not my mother tongue.