Two words of three letters do form the center of L_A and L_B (L_A meaning Ex.20.3-17(letters position) and L_B : Deu.5.7-21). In total these two words appear at center exactly seven time by keeping their letters equidistant.

By the way, in hebrew, ה (center of L_B) is also the number 5 and ב (center of L_A) is also the number 2 which add up to 7 (and corresponds to 5 words in normal reading direction plus two words in counter-direction).

Lastly, in L_A the word "Shabbat" appears in plain text whereas in L_B the word "tohu" appears well in the center of the entire text but as the last two letters of the word אתה  and the first letter of the word ובנך which litterally mean "you and your son" (therefore the word "tohu" escapes the normal reading view).