in v0.12 https://github.com/bitcoin/bitcoin/pull/7081 (by @luke-jr) was merged adding `-bytespersigop` (with default of 20).

this is preventing simple bare multisig transactions from being accepted into mempool when the size is < 400 bytes.  
eg; https://gist.github.com/rubensayshi/ac4f617207f7a50559e85d61c05800be

from 1-of-7 and onwards they are accepted because the ratio of bytes:sigops is high enough.  
also having 2 or more inputs will work because it again tips the ratio of bytes:sigops over.

the reason mainly being that `GetLegacySigOpCount` calls `GetSigOpCount` with `fAccurate=false`.

It looks like changing `GetLegacySigOpCount` to use `fAccurate=true` would cause side effects in the few other places (`ConnectBlock`, `CheckBlock`, `CreateNewBlock`) and simply adding `fAccurate` as arg to `GetLegacySigOpCount` would affect the value stored in `CTxMemPoolEntry.sigOpCount` which in turn affects a bunch of other things.

{
    setEntries s;
    if (add && mapLinks[entry].parents.insert(parent).second) {
        cachedInnerUsage += memusage::IncrementalDynamicUsage(s);
    } else if (!add && mapLinks[entry].parents.erase(parent)) {
        cachedInnerUsage -= memusage::IncrementalDynamicUsage(s);
    }
}
const CTxMemPool::setEntries & CTxMemPool::GetMemPoolParents(txiter entry) const
{
    assert (entry != mapTx.end());
    txlinksMap::const_iterator it = mapLinks.find(entry);
    assert(it != mapLinks.end());
    return it->second.parents;
}
const CTxMemPool::setEntries & CTxMemPool::GetMemPoolChildren(txiter entry) const
{
    assert (entry != mapTx.end());
    txlinksMap::const_iterator it = mapLinks.find(entry);
    assert(it != mapLinks.end());
    return it->second.children;
}
CFeeRate CTxMemPool::GetMinFee(size_t sizelimit) const {