The best way to achieve this would be to use calculation fields for your relationship on each side, and both calculations only displaying the first three characters from the employee position number.
So in both tables create a calculation called _PositionKey [number] and with the following calc, changing according to the name of the appropriate field in both tables.
left ( position# ; 3 )
And then make a join between both _PositionKey fields in both tables, and this should do the trick.
I hope this helps
If there is any possibility that future use of the system might result in number ranges where the first three digits are NOT the same, you might try the following:
Define number fields: MinPosition and MaxPosition.
Define your relationship with two pairs of matching fields:
Position# > MinPosition AND
Position# < MaxPosition
now you can handle a greater range of possible values.