Hi ,
As per my understanding, you want to use 3 decimals when the value is lessthan One(1) and want to use 1 decimal format when the value is Greter than One(1).. If this is the case then follow the below steps to acheive your requirement.
Right click on the Field and select format field > Number
select Customize button and select Formula buttor (X-2) for Decimal Filed and write the below logic
if (Database_field) > 1 then
1
else
3
This may help you.
--Praveen G