The <BEAT and BEAT> buttons on the TRAKTOR KONTROL X1 MK1 always perform a beatjump with the size of one beat, regardless of the loop size selection in TRAKTOR's user interface.
Selecting the X1 in the Device list of TRAKTOR's Controller Manager, you can find the corresponding entries in the assignment table (sort by Control column to get the same view):
To customize the size of the beatjump with another fixed value, you can change it with Set to value for each of the marked assignments as indicated in the screenshot above. The value Loop will make the Beatjump dependant on the current Loop size setting.
In case you want the buttons to not change the size of the beatjump and have it depended on the selection in the Advanced Panel of the Decks, just delete the four assignments one after the other by the Delete command right under the Assignment table (see screenshot above).
To restore the default assignments, just hit the Restore button in the Traktor Kontrol X1 tab in the Preferences.