leaseweb setup the PTR record as hosted-by.leaseweb.com on all IP's - this is valid. They do not however add a matching A record to that IP.
If you resolve hosted-by.leaseweb.com it is 83.149.80.111. In turn this IP resolves to
www.leaseweb.com (in-addr.arpa)
This is a valid setup but an illegal rDNS. The only valid rDNS for 83.149.80.111 is
www.leaseweb.com, all the others are illegal but valid and wont resolve via in-addr.arpa.
So yes you can set all your PTR records to anything.yourdomain.com but they will not resolve over rDNS unless there is a matching A record.
Ive used leaseweb for many years and everytime i ask for a new IP they set the default PTR to hosted-by.leaseweb.com. Perfectly valid and it resolves to an IP, but the reverse on the IP is
www.leaseweb.com so its doesnt work as a rDNS.
Hope this is useful, when i talk about reverse dns i tend to find myself talking in repeating circles :P