Tongue blocking using a neck harmonica holder

Hi David.  I am new to learning harmonica and also play guitar.  I am keen to be able to play the two at the same time using a neck holder.  However I find it is well nigh impossible to tongue block using the upper part of the tongue, instead I am using the lower part just underneath the tip of the tongue.  This seems to work fine but am I storing up problems doing it this way?  Many thanks for your help.