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.

static const CAmount HIGH_TX_FEE_PER_KB = 0.01 * COIN;
static const CAmount HIGH_MAX_TX_FEE = 100 * HIGH_TX_FEE_PER_KB;
static const unsigned int DEFAULT_MAX_ORPHAN_TRANSACTIONS = 100;
static const int64_t ORPHAN_TX_EXPIRE_TIME = 20 * 60;
static const int64_t ORPHAN_TX_EXPIRE_INTERVAL = 5 * 60;
static const unsigned int DEFAULT_ANCESTOR_LIMIT = 25;
static const unsigned int DEFAULT_ANCESTOR_SIZE_LIMIT = 101;
static const unsigned int DEFAULT_DESCENDANT_LIMIT = 25;
static const unsigned int DEFAULT_DESCENDANT_SIZE_LIMIT = 101;
static const unsigned int DEFAULT_MEMPOOL_EXPIRY = 72;
static const unsigned int MAX_BLOCKFILE_SIZE = 0x8000000; 
static const unsigned int BLOCKFILE_CHUNK_SIZE = 0x1000000; 
static const unsigned int UNDOFILE_CHUNK_SIZE = 0x100000; 
static const int MAX_SCRIPTCHECK_THREADS = 16;
static const int DEFAULT_SCRIPTCHECK_THREADS = 0;
static const int MAX_BLOCKS_IN_TRANSIT_PER_PEER = 16;
static const unsigned int BLOCK_STALLING_TIMEOUT = 2;
/** Number of headers sent in one getheaders result. We rely on the assumption that if a peer sends
 *  less than this number, we reached its tip. Changing this value is a protocol upgrade. */
static const unsigned int MAX_HEADERS_RESULTS = 2000;
/** Size of the "block download window": how far ahead of our current height do we fetch?
 *  Larger windows tolerate larger download speed differences between peer, but increase the potential
 *  degree of disordering of blocks on disk (which make reindexing and in the future perhaps pruning
 *  harder). We'll probably want to make this a per-peer adaptive value at some point. */
static const unsigned int BLOCK_DOWNLOAD_WINDOW = 1024;
static const unsigned int DATABASE_WRITE_INTERVAL = 60 * 60;
static const unsigned int DATABASE_FLUSH_INTERVAL = 24 * 60 * 60;
static const unsigned int MAX_REJECT_MESSAGE_LENGTH = 111;
static const unsigned int AVG_LOCAL_ADDRESS_BROADCAST_INTERVAL = 24 * 24 * 60;
static const unsigned int AVG_ADDRESS_BROADCAST_INTERVAL = 30;