dependencies - How to make Apt/Aptitude prefer a more recent virtual package over a real one

I've recently built a package which provides multiple virtual ones, more specifically snmp which provides libsnmp-base, libsnmp30 and so on:

• Version: 5.8~git20160427.8d07349f-14


• Depends: ...


• Provides:
  snmp,libsnmp-base,libsnmp-dev,libsnmp30,python-snmp,snmpd,snmptrapd,tkmib


• Conflicts:
  libsnmp-base,libsnmp-dev,libsnmp30,python-snmp,snmpd,snmptrapd,tkmib


• Replaces:
  libsnmp-base,libsnmp-dev,libsnmp30,python-snmp,snmpd,snmptrapd,tkmib

It is installed on my system & provided on my online PPA.
When I try to install another package (php7.0-snmp) which depends on libsnmp30 & libsnmp-base, Apt offers me to uninstall snmp in order to install the required dependencies.
It seems that Apt always prefers real packages over virtual ones, despite the facts that:

• the virtual ones have a more recent version


• they are already installed

Aptitude offers more solutions, but none involves the preferred & most logical one: keep snmp because it already offers the most recent needed dependencies:

sudo aptitude install php7.0-snmpThe following NEW packages will be installed:
  libsnmp30{a} php7.0-snmp
0 packages upgraded, 2 newly installed, 0 to remove and 1 not upgraded.
Need to get 832 kB of archives. After unpacking 3,382 kB will be used.
The following packages have unmet dependencies:
 snmp : Conflicts: libsnmp30 but 5.7.3+dfsg-1ubuntu4 is to be installed.
The following actions will resolve these dependencies:
     Remove the following packages:
1)     snmp
     Install the following packages:
2)     libsnmp-base [5.7.3+dfsg-1ubuntu4 (xenial)]
Accept this solution? [Y/n/q/?] n
The following actions will resolve these dependencies:
     Keep the following packages at their current version:
1)     libsnmp30 [Not Installed]
2)     php7.0-snmp [Not Installed]
Accept this solution? [Y/n/q/?] n
The following actions will resolve these dependencies:
     Install the following packages:
1)     libsnmp-base [5.7.3+dfsg-1ubuntu4 (xenial)]
     Downgrade the following packages:
2)     snmp [5.8~git20160427.8d07349f-14 (now) -> 5.7.3+dfsg-1ubuntu4 (xenial)]
Accept this solution? [Y/n/q/?] n
*** No more solutions available ***

How can I install php7.0-snmp without having to uninstall snmp?