Crosses are not all similar... you have variations and some these variations have "meanings"... For example, we have some crosses that are "inverted" and are related with atheists in XVIII century. You have the crosses from the "Order of Christ" used by Portuguese navigators, that are unique, and identifies the Order that was formed in Portugal by European fugitives and portuguese Templars under the protection of the portuguese King (they change the name from Templars to Order of Christ to escape from Pope and French persecutions).
If you say that all crosses are equal, so you don't know nothing about history...
The carved cross in France it's different because have a "head" on the top, down to the left side, and open arms... It's different from other crosses carved, and if it's different it's because have a meaning (we just don't know the meaning for now).
The cross found on OI, it's different from usual crosses, because have a "head" on the top, down to the left side, and open arms... It's different from other crosses that people carry on past times, and if it's different it's because have a meaning (we just don't know the meaning for now).
This can be a coincidence... or not... If you have 2 special exceptions it's normal to try to relate them (but can be a coincidence anyway)...
NOW, we have another cross, carved in a cave associated with Templars, that have a "head" on the top, down to the left side, and open arms...
AGAIN, This can be a coincidence, or not... the carved cross in Royston it's very similar to the French cross... this is an evidence...
What all of these means? I don't know... But I'm 100% sure that all crosses have a special meaning (probably the same meaning), but this don't mean that all are related.
My opinion (and it's just an opinion) the cross with head means the crucifixion of Christ like it's usual on the churches altars. Christians usually pray in front of these crosses (on them knees)... So I think that these carved crosses are representations of altars (like a diy altar to pray). The OI cross, can represent the same, being like a "portable altar" for explorers that want to pray in places where are no churches)... My "theory" indicates that all crosses have the same meaning (explain why are all similar), but not related...
The best
Ricardo