Holograms [witherskulls are sometimes visible]

/summon WitherSkull ~ ~2 ~

{direction:[0.0,0.0,0.0],ExplosionPower:0,CustomName:"EXAMPEL",CustomNameVisible:true}

Mapmakers use this for holographic text ,but:
-the witherskull ist visible in the moment when you´re spawning it
-it will plink(get visible and invisible again) randomly

personal problem
I would like to use ,to make RPG Healthbars for mobs and players but if you´re constandly summoning this things above an entitys head and emeadiatly kill it ,you´ll have a nice healthbar ,exept that your still seeing the witherskull above you cause it´s always visible for a second

my concept is based on this video: https://www.youtube.com/watch?v=bUfYmBUbmfc&list=PLPETk8BsQC2eq7mV7vuXtuXc_5qs31CIx&index=83
exept that i´m using this
/execute @e[score_healthbar=20,score_healthbar_min=20] ~ ~ ~ /summon WitherSkull ~ ~2 ~ {ActiveEffects:[

{Id:14,Amplifier:1,Duration:3217,Ambient:1,ShowParticles:false}

],direction:[0.0,0.0,0.0],ExplosionPower:0,CustomName:"♥♥♥♥♥♥♥♥♥♥",CustomNameVisible:true}
instead of using the entitydata commmands Ethos used ,so that my one is able to display players aswell.