OP, you are the keeper and leaseholder.
The sign purports to charge a driver - which includes you - a parking charge of £100 for not parking wholly on a parking space or on roadways i.e.the 'Estate'.
These parking spaces are allocated to leaseholders.
IMO, a RK/leaseholder cannot be held accountable to two masters.
So, if you authorise a driver to use your bay and they do not park wholly within then what's their and your liability? £100 as RK or the landlord's wrath or whatever other sanction is available to them under the lease?
Both?
So, if you tell a driver to park your vehicle 'on the Estate except on the [your] parking space' then who is liable to whom and for what?
IMO, the scope of the signs excludes leaseholders whether directly or indirectly unless there are provisions within your lease to the contrary.