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.

#include "policy/policy.h"
#include "main.h"
#include "tinyformat.h"
#include "util.h"
#include "utilstrencodings.h"
#include <boost/foreach.hpp>
    /**
     * Check transaction inputs to mitigate two
     * potential denial-of-service attacks:
     * 
     * 1. scriptSigs with extra data stuffed into them,
     *    not consumed by scriptPubKey (or P2SH script)
     * 2. P2SH scripts with a crazy number of expensive
     *    CHECKSIG/CHECKMULTISIG operations
     *
     * Why bother? To avoid denial-of-service attacks; an attacker
     * can submit a standard HASH... OP_EQUAL transaction,
     * which will get accepted into blocks. The redemption
     * script can be anything; an attacker could use a very
     * expensive-to-check-upon-redemption script like:
     *   DUP CHECKSIG DROP ... repeated 100 times... OP_1
     */
bool IsStandard(const CScript& scriptPubKey, txnouttype& whichType)